Synthesis of novel tryptophan derivatives of potential biological activity

Abstract

Tryptophan methyl ester 2 reacts with ethyl cyanoacetate to form acetonitrilocarbonyltryptophan methylester 3. The latter reacts with cyanomethylene re-agents, hydrazines, cyanomethylenes and sulfur to form the corresponding α-pyrido-3-indolopropanoate derivatives 6a,b, pyrazolyltryptophan methyl ester deriva-tives 8a,b and thiophenotryptophan methyl ester derivatives 10a,b, respectively. Also compound 3 reacts with benzaldehyde to give the condensated product 12. The reactivity of the latter product towards chemical reagents was studied to form pyridine, pyrazole and isoxazole derivatives.

Full text

J. Chil. Chem. Soc., 54, Nº 2 (2009)
175
SYNTHESIS OF NOVEL TRYPTOPHAN DERIVATIVES OF POTENTIAL BIOLOGICAL ACTIVITY
RAFAT M. MOHAREBA,B*, NADIA A. LOUCAC, GAMAL A. ELMEGEEDC AND HANAA Y. HANAC
a Departament of Organic Chemistry, Faculty of Pharmacy, October University for Modem Sciences and Arts (MSA), El-Wahaat Road, October City, Egypt
bChemistry Department, Faculty of Science, Cairo University, Giza, Egypt
cHormone Department, National Research Centre, Dokki, Giza, Egypt
(Received: May 27, 2008 -Accepted: December 12, 2008)
ABSTRACT
Tryptophan methyl ester 2 reacts with ethyl cyanoacetate to form acetonitrilocarbonyltryptophan methylester 3. The latter reacts with cyanomethylene re-
agents, hydrazines, cyanomethylenes and sulfur to form the corresponding α-pyrido-3-indolopropanoate derivatives 6a,b, pyrazolyltryptophan methyl ester deriva-
tives 8a,b and thiophenotryptophan methyl ester derivatives 10a,b, respectively. Also compound 3 reacts with benzaldehyde to give the condensated product 12.
The reactivity of the latter product towards chemical reagents was studied to form pyridine, pyrazole and isoxazole derivatives.
Keywords: Teyptophane, pyrazd, pyridine, 1, 3 - oxazine.
e.mail: raafat_mohareb@yahoo.com
INTRODUCTION
The development of potential therapeutic agents based on the structure
of peptides has stimulated an interest in the design and synthesis of unnatural
amino acids [1-3]. Thus, numerous chemical transformations of amino acids
have been reported [4]. Indole and it’s derivatives have been a topic of research
interest for over a century [5,6]. This, is in part, due to the fact that indole
moieties are found in a variety of naturally occurring compounds that exhibit
various physiological properties [7,8]. Tryptophan is one of the most important
amino acids which containing indole moiety. However, to our knowledge, few
investigations have been reported concerning its uses in the formation of cyclic
tryptophan derivatives [9-12]. The reaction of tryptophan with cyanoacetates
is known to produce cyanoamides in the aim of forming photo-active cross-
linking bioprobes [13,14]. In view of these observations and in continuation
with studies involving the synthesis of unusual hormones and amino acids de-
rivatives [15-17], we have used in this study, L-tryptophan is used to form new
heterocyclic compounds of potential biological activities.
RESULTS AND DISCUSSION
The reaction of tryptophan (1) with methanol in acetyl chloride solution
afforded the corresponding tryptophan methyl ester 2 (Scheme 1). Compound
2 reacted with an equimolar amount of ethyl cyanoacetate in 1,4-dioxan under
reux to give the methyl α-imino(acetonitrilocarbamido)-3-indolopropanoate
(3) via elimination of ethanol. The mass spectrum of compound 3 showed mo-
lecular ion peak at m/z 286 (25%). The IR spectrum of compound 3 revealed
the presence of NH stretching at v 3400-3360 cm-1, one CN group stretching at
v 2220 cm-1 and two C=O groups stretching at v 1730 and 1680 cm-1. Also the
1H NMR spectrum of compound 3 showed two D2O-exchangeable singlets at
δ 8.65 and 8.76 for the two NH groups (cf. experimental section). Moreover,
the 13C NMR spectrum showed δ 22.6 (CH3), 28.9, 44.2 (2 CH2), 50.2 (CH),
115.1, 116.7, 118.4, 120.4, 121.4, 122.6, 142.6 (pyrole, benzene C), 172.6,
174.8 (2 C=O).
To improve the pharmaceutical properties of the tryptophan molecule, we
have outlined the synthesis of several indole derivatives containing heterocy-
clic moiety. Therapeutic agents containing pyridine, thiophene, and pyrazole
moieties have attracted the attention of researchers in pharmaceutical chem-
istry; these heterocycles have been found to show various biological activities
[18,19]. Compound 3 seemed to be an interest candidate for further chemical
transformations to form indole derivatives with potential biological activity.
The reactivity of compound 3 towards the reaction with active methylene re-
agents was investigated. Thus, compound 3 reacted with equimolar amount of
either malononitrile (4a) or ethyl cyanoacetate (4b) in ethanolic triethylamine
solution gave the α-pyrido-3-indolopropanoate derivatives 6a,b, respectively.
Formation of the latter products took place via the intermediate formation of
5a,b which underwent ready intramolecular cyclization to give compounds
6a,b (Scheme 2). The IR spectrum of each of 6a and 6b showed two CN groups
stretching at v 2200 and 2225 cm-1, respectively. The 1H NMR of compound
6a showed a singlet at δ 4.62 (4H, D2O-exchangeable) for the two NH2 groups
while that of compound 6b showed a singlet at δ 4.41 (2H, D2O-exchangeable)
for one NH2 group and a singlet at δ 10.05 for the OH group. Moreover, each
of compounds 6a,b showed a singlet at δ 6.23 and 6.34, respectively for the
pyridine ring proton at C-3 (cf. experimental section).
The study also extended to the reactivity of compound 3 towards nitrogen
nucleophilic reagents. Thus, compound 3 reacted with equimolar amounts of
either hydrazine hydrate or phenylhydrazine in reuxing ethanol containing a
catalytic amount of triethylamine to give the corresponding pyrazolyltrypto-
phan methyl ester derivatives 8a,b. The reaction took place via a simple ad-

J. Chil. Chem. Soc., 54, Nº 2 (2009)
176
dition of hydrazine hydrate or phenylhydrazine to the CN group in compound
3 to give the intermediates 7a,b which readily afforded compounds 8a,b via
water elimination (Scheme 2). Moreover, compound 3 reacted with hydrox-
ylamine hydrochloride in cold ethanolic sodium acetate solution to give the
corresponding oxadiazinomethylenoindole derivative 9 (Scheme 2). Structures
of compounds 8a,b and 9 were supported by their compatible analytical and
spectral data (cf. experimental section).
The reaction of compound 3 with equimolar amount of benzaldehyde in
ethanolic triethylamine solution under reux afforded the condensated product
benzalacetonitrilocarbonyltryptophan methyl ester derivative 12 (Scheme 4).
The reactivity of the α,β-unsaturated nitrile moiety of compound 12 towards
the reaction with various chemical reagents was investigated. Thus, 12 reacted
with either malononitrile 4a or ethyl cyanoacetate 4b in reuxing ethanolic
triethylamine solution to give the methyl α-pyrido-1-yl-3-indolopropanoate
derivatives 14a,b, respectively via the intermediacy of 13a,b (Scheme 4). The
IR spectrum of compound 14a revealed the presence of two CN groups at v
2220 and 2215 cm-1 and the 1H NMR spectrum of compound 14a showed two
D2O-exchangeable singlets at δ 4.46 (2H) and δ 11.02 (1H) corresponding to
the NH2 and NH groups, respectively. The mass spectrum of compound 14b
showed a molecular ion peak at m/z 486 (35%) and the 1H NMR spectrum of
14b revealed a triplet at δ 1.33 and a quartet at δ 4.32 which is characteristic to
ethyl ester group (cf. experimental section).
Compound 3 reacted with equimolar amounts of either malononitrile 4a
or ethyl cyanoacetate 4b and elemental sulfur in ethanolic triethylamine solu-
tion under reux to afford the corresponding thiophenotryptophan methyl ester
derivatives 10a,b (Scheme 3). The IR spectrum of compound 10a revealed the
presence of two CN groups stretching at v 2210 and 2225 cm-1 and the 1H NMR
spectrum revealed the presence of D2O-exchangeable singlet (2H) at δ 4.58 for
the NH2 group and two D2O-exchangeable singlets at δ 10.78 (1H) and δ 11.94
(1H) for the two NH groups. On the other hand, the IR spectrum of 10b showed
the presence of one CN group stretching at v 2200 cm-1 and its 1H NMR spec-
trum showed a triplet at δ 1.23 beside a quartet at δ 4.24 due to the ethyl ester
group, in addition to the NH2 and the two NH singlet signals at δ 6.50, 10.71
and 10.88, respectively. The cyanomethylene moiety of compound 3 coupled
easily with benzenediazonium chloride in cold ethanolic sodium acetate solu-
tion to give the phenylhydrazo derivative 11 based on 1H NMR spectrum which
showed, beside the expected chemical shifts, three NH singlets at δ 9.25 and
9.97-9.99 (D2O-exchangeable) (Scheme 3).
The reactivity of compound 12 towards the reaction with nucleophilic re-
agents was investigated. Thus, the reaction of 12 with equimolar amounts of
either hydrazine hydrate or phenylhydrazine in ethanolic triethylamine solution
under reux afforded the corresponding carbonylpyrazolotryptophan methyl
ester derivatives 15a,b, respectively (Scheme 5). Similarly compound 12 re-
acted with hydroxylamine hydrochloride in ethanol containing sodium acetate
solution to afford the isooxazolotryptophan methyl ester derivative 16 (Scheme
5). The chemical structures of compounds 15a,b and 16 were conrmed via the
analytical and spectral data (cf. experimental section).

J. Chil. Chem. Soc., 54, Nº 2 (2009)
177
Tryptophan (1) reacted with an equimolar amount of ethyl cyanoacetate in
reuxing dimethylformamide solution to give the acetonitrilocarbonyl trypto-
phan 17 (Scheme 5). The IR spectrum of compound 17 revealed the presence of
two NH groups stretching at v 3430-3385 cm-1, and one CN group stretching at
v 2220 cm-1 in addition to two C=O groups stretching at v 1705 and 1680 cm-1.
Also the 1H NMR spectrum of compound 17 showed two singlets at δ 8.75 and
8.82 (D2O-exchangeable) for the two NH groups and a singlet at δ 11.15 for the
OH group (cf. experimental section). Compound 17 reacted with an equimolar
amount of benzaldehyde in ethanol/piperidine solution under reux to afford
the condensed product benzaloacetonitrilocarbonyl-tryptophan 18 (Scheme 5).
Moreover, compound 17 easily coupled with benzenediazonium chloride in
cold ethanolic sodium acetate solution to afford the phenylhydrazo derivative
19 (Scheme 5), based on 1H NMR spectrum which showed, beside the expected
chemical shifts, three NH singlets at δ 8.51 and 9.32-9.36 (D2O-exchangeable).
The structures of the latter products 18 and 19 were conrmed based on their
compatible elemental and spectral analyses (cf. experimental section).
EXPERIMENTAL SECTION
The starting pure powder of L-tryptophan was purchased from Sigma
Company, USA. The appropriate precautions in handling moisture sensitive
compounds were undertaken. All melting points of the newly synthesized com-
pounds were measured using an electrothermal capillary melting point appa-
ratus and are uncorrected. The IR spectra are expressed in cm-1 and recorded
in KBr pellets on a Pa-9721 IR spectrometer (Shimadzu, Japan). 1H- and 13C
NMR spectra were obtained on a Varian EM-390 90 MHz spectrometer in
DMSO-d6 as solvent, using TMS as internal reference and chemical shifts
(δ) are expressed in ppm. Mass spectra were recorded on a GCMS-QP 1000
Ex spectra mass spectrometer operating at 70 eV Equipment (Germany). El-
emental analyses were preformed with all nal compounds by Microanalytical
Data Unit at The National Research Centre, Giza, Egypt. The reactions were
followed using TLC analyses which were performed using Merck 60 F254
aluminum sheets and visualized by UV light (254 nm). Although tryptophan
methyl ester is commercially available in the hydrochloride form we preferred
to syntheses the native methyl ester via the procedure indicated below.
Methyl α-amino-3-indolopropanoate (2). To a solution of tryptophan 1
(10.2 g, 0.05 mol) in methanol (5 mL) equivalent amount of acetylchloride
(3.77 mL, 0.05 mol) in methanol (30 mL) was added drop wise with stirring
at 0°C. The reaction mixture was stirred for 24 h, and then evaporated under
vacuum. The formed solid product neutralized by sodium carbonate solution (1
N), extracted by chloroform and dried by anhydrous sodium sulfate. The solid
product formed after evaporation of the solvent, ltered off, dried and crystal-
lized from methanol. White crystals, yield 55% (6.0 g), mp 152-153°C. IR (v/
cm-1): 3450-3235 (NH2, NH), 3050 (CH-aromatic) 2985, 2865 (CH3, CH2) 1730
(C=O), 1620 (C=C). 1H NMR (δ ppm): 3.35 (s, 3H, CH3), 3.43 (m, 2H, CH2),
3.75 (m, 1H, CH), 6.57 (s, 2H, NH2, D2O-exchangeable), 6.64 (s, 1H, CH),
7.51 (m, 4H, C6H4), 8.92 (s, 1H, NH, D2O-exchangeable). MS (m/z, %): 218
(M+˙, 45%). Anal. Calcd. for C12H14N2O2 (218.26): C, 66.03; H, 6.46; N, 12.83.
Found: C, 65.79; H, 6.25; N, 12.52.
Methyl α-imino(acetonitrilocarbamido)-3-indolopropanoate (3). To a
solution of 2 (1.09 g, 0.005 mol) in 1,4-dioxan (30 mL), equivalent amount
of ethyl cyanoacetate 4b (0.56 g, 0.005 mol) was added. The reaction mixture
was heated under reux for 3h. The solid product formed by evaporation un-
der vacuum was ltered off, dried and crystallized. White crystals from diox-
ane, yield 75% (1.07 g), mp 128-130°C. IR (v/cm-1): 3400-3360 (2NH), 3050
(CH-aromatic), 2985, 2659 (CH3, CH2), 2220 (CN), 1730, 1680 (2C=O), 1620
(C=C). 1H NMR (δ ppm): 3.38 (s, 3H, CH3), 3.45 (m, 2H, CH2), 3.48 (s, 2H,
CH2CN), 3.78 (m, 1H, CH), 6.95 (s, 1H, CH), 7.01-7.49 (m, 4H, C6H4), 8.65,
8.76 (2s, 2H, 2NH, D2O-exchangeable). 13C NMR (δ): 22.6 (CH3), 28.9, 44.2
(2 CH2), 50.2 (CH), 115.1, 116.7, 118.4, 120.4, 121.4, 122.6, 142.6 (pyrole,
benzene C), 172.6, 174.8 (2 C=O). MS (m/z, %): 286 (M++1), 25%), 260 (M+˙-
CN, 25%), 203 (M+˙-NHCOCH2CN, 23%), 130 (indolomethylene fragment,
C9H8N, 100%). Anal. Calcd. for C15H15N3O3 (285.30): C, 63.15; H, 5.30; N,
14.73. Found: C, 63.42; H, 5.37; N, 14.39.
Methyl α-(2,4-diamino-5-cyano-6-oxopyrido-1-yl)-3-indolopropanoate
(6a), Methyl α-(4-Amino-5-cyano-2-hydroxy-6-oxopyido-1-yl) -3-indolo-
propanoate (6b)
General Procedure
To a solution of Compound 3 (1.42 g, 0.005 mol) in ethanol (30 mL),
containing a catalytic amount of triethylamine (1 mL, 0.01 mol), equivalent
amount of either malononitrile 4a (0.33 g, 0.005 mol) or ethyl cyanoacetate 4b
(0.56 g, 0.005 mol) was added. The reaction mixture in each case was heated
under reux for 3h and then was cooled at room temperature, poured over ice/
water mixture and neutralized with dilute hydrochloric acid. The formed solid
product, in each case ltered off, dried and crystallized from the appropriate
solvent.
Compound 6a: Yellow crystals, from MeOH, yield 77% (1.35g), mp
150-152°C. IR (v/cm-1): 3450-3250 (2NH2, NH), 2980, 2865 (CH3, CH2), 2200
(CN), 1730, 1690 (2C=O). 1H NMR (δ ppm): 3.33 (s, 3H, CH3), 3.43 (m, 2H,
CH2), 3.70 (m, 1H, CH), 4.62 (s, 4H, 2NH2, D2O-exchangeable), 6.23 (s, 1H,
C3-pyridine ring proton), 6.62 (s, 1H, CH), 7.00-7.32 (m, 4H, C6H4), 10.87
(s, 1H, NH, D2O-exchangeable). MS (m/z, %): 351 (M+˙, 55%), 325 (M+˙-
CN, 35%), 130 (indolomethylene fragment, C9H8N, 100%). Anal. Calcd. for
C18H17N5O3 (351.36): C, 61.53; H, 4.87; N, 19.93. Found: C, 61.21; H, 4.73;
N, 19.67.
Compound 6b: Pale yellow crystals, from MeOH, yield 82% (1.44 g),
mp 198-199°C. IR (v/cm-1): 3450-3250 (NH2, NH), 3050 (CH-aromatic), 2225
(CN), 1730, 1700 (2C=O), 1630 (C=C). 1H NMR (δ ppm): 3.38 (s, 3H, CH3),
3.43 (m, 2H, CH2), 3.75 (m, 1H, CH), 4.41 (s, 2H, NH2, D2O-exchangeable),
6.34 (s, 1H, C3-pyridine ring proton), 6.82 (s, 1H, CH), 7.11-7.54 (m, 4H,
C6H4), 10.05 (s, 1H, OH). Anal. Calcd. for C18H16N4O4 (352.35): C, 61.35; H,
4.57; N, 15.90. Found: C, 61.19; H, 4.28; N, 15.73.
Methyl α-imino(5-aminopyrazolo-3-yl)-3-indolopropanoate (8a)
Methylα-imino(5-amino-2-phenylpyrazolo-3-yl)-3-indolopropanoate
(8b)
General Procedure. To a solution, of compound 3 (1.42 g, 0.005 mol) in
ethanol (30 mL), containing a catalytic amount of triethylamine (2 mL, 0.02
mol), equivalent amount of either hydrazine hydrate (0.25 g, 0.005 mol) or
phenylhydrazine (0.54 g, 0.005 mol) was added. The reaction mixture in each
case was heated under reux for 5 h and then was cooled at room temperature,
poured over ice/water mixture and neutralized with dilute hydrochloric acid.

J. Chil. Chem. Soc., 54, Nº 2 (2009)
178
The formed solid product, in each case, was ltered off, washed with water and
crystallized from the appropriate solvent.
Compound 8a: White crystals, from EtOH, yield 72% (1.08 g), mp 154-
155°C. IR (v/cm-1): 3450-3250 (NH2, 3NH), 3050 (CH-aromatic), 2985, 2865
(CH3, CH2), 1720 (C=O), 1660 (C=N), 1620 (C=C). 1H NMR (δ ppm): 3.35
(s, 3H, CH3), 3.46 (m, 2H, CH2), 3.73 (m, 1H, CH), 4.50 (s, 2H, NH2, D2O-
exchangeable), 5.83 (s, 1H, CH pyrazole), 6.51 (s, 1H, CH), 6.98-7.40 (m, 4H,
C6H4), 9.83, 10.80, 10.92 (3s, 3H, 3NH, D2O-exchangeable). Anal. Calcd. for
C15H17N5O2 (299.33): C, 60.18, H, 5.72, N, 23.39. Found: C, 59.90; H, 5.43;
N, 23.64.
Compound 8b: Brown crystals, from EtOH, yield 75% (1.40 g), mp. 90-
91°C. IR (v/cm-1): 3400-3250 (NH2, 2NH), 3050 (CH-aromatic), 2985, 2865
(CH3, CH2), 1730 (C=O), 1660 (C=N), 1620 (C=C). 1H NMR (δ ppm): 3.40
(s, 3H, CH3), 3.51 (m, 2H, CH2), 3.74 (m, 1H, CH), 4.23 (s, 2H, NH2, D2O-
exchangeable), 5.83 (s, 1H, CH pyrazole), 6.33 (s, 1H, CH), 7.32-7.55 (m, 9H,
C6H4, C6H5), 10.80, 10.92 (2s, 2H, 2NH, D2O-exchangeable). MS (m/z, %):
374 (M+˙-1; 34%), 298 (M+˙- C6H5, 57%), 77 (C6H5; 70%). Anal. Calcd. for
C21H21N5O2 (375.43): C, 67.18; H, 5.62; N, 18.65. Found: C, 67.17; H, 5.49;
N, 18.52.
3-Acetonitrilo-6-hydroxy-3-methylenoindolo-2,1,4 oxadiazine (9). To
a solution of compound 3 (1.42 g, 0.005 mol) in ethanol (30 mL), containing
a catalytic amount of sodium acetate (1.0 g) equivalent amount of hydroxy-
lamine hydrochloric acid (0.35 g, 0.005 mol) in H2O (5 mL) was added with
stirring. The reaction mixture was stirred with warming for 30min, left to cool
to 20 °C. The formed solid product was triturated ice/water mixture, collected
by ltration and crystallized from MeOH. White crystals, yield 73% (0.97 g),
mp 94-95°C. IR (v/cm-1): 3300-3200 (2NH, OH), 3050 (CH-aromatic), 2985,
2865 (CH3, CH2), 2200 (CN), 1660 (C = N), 1620 (C = C). 1H NMR (δ ppm):
1.25 (s, 2H, CH2), 3.91 (s, 2H, CH2), 6.64 (s, 1H, CH), 7.00-7.71 (m, 4H, C6H4),
9.22, 9.52 (2s, 2H, 2NH, D2O-exchangeable), 10.89 (s, 1H, OH). 13C NMR (d):
20.3, 21.6 (2CH2), 88.4 (oxadiazine C-4), 118.7, 119.4, 120.6, 120.9, 121.5,
130.4, 136.9 (benzene, pyrrole C), 118.7 (CN). 179.8 (oxadiazine C-3). Anal.
Calcd. for C14H12N4O2 (268.28). C, 62.68; H, 4.50; N, 20.83. Found: C, 62.59;
H, 4.53; N, 20.77.
Methyl α-N-(5-amino-2,4-dicyanothiopheno-3-yl)-3-indolopropanoate
(10a)
Methylα-N-(ethyl 5-amino-2-cyanothiopheno-3-yl-4-carboxylate)-3-
indolo-propanoate (10b)
General Procedure
To a mixture of compound 3 (1.42 g, 0.005 mol), elemental sulfur (0.16
g, 0.005mol) and either malononitrile 4a (0.33 g, 0.005 mol) or ethyl cyanoac-
etate 4b (0.56 g, 0.005 mol) in ethanol (30 mL), triethylamine (0.5 mL, 0.005
mol) was added. The reaction mixture in each case was heated under reux for
4 h and then was cooled at room temperature, poured over ice/water mixture
and neutralized with dilute hydrochloric acid. The formed solid product was
ltered off, dried and crystallized from the appropriate solvent.
Compound 10a: Brown crystals, from MeOH, yield 73% (1.33 g), mp 106-
107°C. IR (v/cm-1): 3400-3250 (NH2, 2NH), 3050 (CH-aromatic), 2965, 2865
(CH3, CH2), 2210, 2225 (2CN), 1730 (C = O), 1620 (C = C). 1H NMR (δ ppm):
3.39 (s, 3H, CH3), 3.53 (m, 2H, CH2), 3.75 (m, 1H, CH), 4.58 (s, 2H, NH2, D2O-
exchangeable), 6.53 (s, 1H, CH), 7.01-7.60 (m, 4H, C6H4) 10.78, 11.94 (2s, 2H,
2NH, D2O-exchangeable). Anal. Calcd. for C18H15N5SO2 (365.42): C, 59.16; H,
4.13; N, 19.16; S, 8.77. Found: C, 58.91; H, 4.05; N, 19.02; S, 8.51.
Compound 10b: Pale brown crystals, from EtOH, yield 75% (1.54g), mp
91-92°C. IR (v/cm-1): 3400-3250 (NH2, 2NH) 3050 (CH-aromatic), 2965, 2865
(CH3, CH2), 2200 (CN), 1730, 1700 (2C=O), 1620 (C=C). 1H NMR (δ ppm):
1.23 (t, 3H, J = 6.8 Hz, ester CH3), 3.41 (s, 3H, CH3), 3.53 (m, 2H, CH2), 3.75
(m, 1H, CH), 4.24 (q, 2H, J = 6.8 Hz, ester CH2), 6.50 (s, 2H, NH2, D2O-
exchangeable), 6.99 (s, 1H, CH), 7.04-7.49 (m, 4H, C6H4), 10.71, 10.88 (2s,
2H, 2NH, D2O-exchangeable). MS (m/z, %): 412 (M+˙, 62%). Anal. Calcd. for
C20H20N4O4S (412.47): C, 58.23; H, 4.88; N, 13.58; S, 7.77. Found: C, 58.11;
H, 4.72; N, 13.43; S, 7.62.
Methyl α-N-(phenylhydrazoacetonitrilocarbamido)-3 indolopropano-
ate (11). A solution of compound 3 (1.42 g, 0.05 mol), in ethanol (30 mL)
containing a catalytic amount of sodium acetate (1.0 g) was cooled to 0-5°C
and then treated gradually with a cold solution of benzenediazonium chloride
(prepared from the appropriate quantities of aniline, HCl and NaNO2). After
addition of the diazonium salt was completed, the reaction mixture was stirred
at room temperature for 30 min. The solid product, separated upon dilution
with cold water, was ltered off, washed with water several times, dried and
crystallized from EtOH to yield 72% (1.40 g) pale brown crystals, mp 94-95°C.
IR (v/cm-1): 3400, 3300 (3NH), 3050 (CH-aromatic), 2985, 2865 (CH3, CH2),
2200 (CN), 1720, 1690 (2C=O), 1660 (C=N), 1630 (C=C). 1H NMR (δ ppm):
1.27 (s, 1H, CH), 3.37 (s, 3H, CH3), 3.47 (m, 2H, CH2), 3.70 (m, 1H, CH), 5.64
(s, 1H, CH), 7.67-7.74 (m, 9H, C6H4, C6H5), 9.25, 9.97-9.99 (3s, 3H, 3NH,
D2O-exchangeable). Anal. Calcd. for C21H19N5O3 (389.41): C, 64.77; H, 4.91;
N, 17.98. Found: C, 64.67; H, 4.89; N, 17.88.
Methyl α-N-(benzaloacetonitrilocarbamido)-3-indolopropanoate (12).
To a solution of compound 3 (1.42 g, 0.005 mol) in ethanol (30 mL), contain-
ing triethylamine (1 mL, 0.01 mol), equivalent amount of benzaldehyde (0.53
g, 0.005 mol) was added. The reaction mixture was heated under reux for 3h.
Then poured over ice/water mixture and neutralized with dilute hydrochloric
acid. The formed solid product ltered off, dried and crystallized from EtOH.
Pale brown crystals, yield 77% (1.43 g), mp 81-82°C. IR (v/cm-1): 3400-3200
(2NH), 3050 (CH-aromatic), 2985, 2865 (CH3, CH2), 2200 (CN), 1720, 1690
(2C=O). 1H NMR (δ ppm): 3.40 (s, 3H, CH3), 3.59 (m, 2H, CH2), 3.72 (m,
1H, CH), 4.10 (s, 1H, CH), 7.08 (s, 1H, CH), 7.31-7.72 (m, 9 H, C6H4, C6H5),
8.42, 10.93 (2s, 2H, 2NH, D2O-exchangeable). MS (m/z, %): 374 (M+˙, 22%),
315 (M+˙-COOCH3, 21%), 284 (M+˙- CHPh, 20%), 130, (indolomethylene frag-
ment, C9H8N, 100%). Anal. Calcd. for C22H19N3O3 (373.41): C, 70.76; H, 5.12;
N, 11.25. Found: C, 70.55; H, 5.11; N, 11.13.
Methyl α-(6-amino-3,5-dicyano-2-oxo-4-phenylpyrido-1-yl) -3-indolo-
propanoate (14a)
Methyl α-(ethyl 6-amino-3-cyano-2-oxo-4-phenylpyrido-1-yl-5-
carboxylate)-3-indolopropanoate (14b)
General Procedure. To a solution of compound 12 (1.86 g, 0.005 mol)
in ethanol (30 mL), containing (1 mL, 0.01 mol), equivalent amount of either
malononitrile 4a (0.33 g, 0.005 mol), or ethyl canoacetate 4b (0.56 g, 0.005
mol) was added. The reaction mixture, in each case, was heated under reux
for 3h then poured over ice/water mixture and neutralized with hydrochloric
acid. The formed solid product, in each case ltered off, dried, and crystallized
from the appropriate solvent.
Compound 14a: yellow crystals, from EtOH, yield 72% (1.58g), mp 118-
120°C. IR (v/cm-1): 3450-3350 (NH2), 3300, 3200 (2NH), 3050 (CH-aromatic),
2985, 2865 (CH3, CH2), 2220, 2215 (2 CN), 1730, 1690 (2C = O). 1H NMR
(δ ppm): 3.39 (s, 3H, CH3), 3.53 (m, 2H, CH2), 3.75 (m, 1H, CH), 4.46 (s, 2H,
NH2, D2O-exchangeable), 6.51, 6.57 (2d, 2H, J = 9.7 Hz, 2CH), 6.60 (s, 1H,
CH), 7.02-7.60 (m, 9 H, C6H5, C6H4), 11.02 (s, 1H, NH, D2O-exchangeable).
13C NMR (δ): 18.9 (CH2), 48.7 (CH3), 55.8 (CH), 80.9, 11.6, 113.4, 115.9,
118.4, 120.1, 122.7, 130.5, 133.8 (benzene, pyrrole C), 118.6, 119.2 (2 CN),
160.3, 170.4 (2CO). Anal. Calcd. for C25H21N5O3 (439.37): C, 68.32; H, 4.81;
N, 15.93. Found: C, 68.25; H, 4.73; N, 15.85.
Compound 14b: White crystals, from dioxane, yield 77% (1.87 g), mp
77-78°C. IR (v/cm-1): 3450-3250 (NH2, NH), 3050 (CH-aromatic), 2985, 2865
(CH3, CH2), 2200, (CN), 1735, 1730, 1700 (3C=O), 1630 (C=C). 1H NMR (δ
ppm): 1.33 (t, J = 6.8 Hz, 3H, ester CH3), 3.45 (s, 3H, CH3), 3.52 (m, 2H, CH2),
3.68 (m, 1H, CH), 4.32 (q, 2H, J = 6.8 Hz, ester CH2), 5.18 (s, 2H, NH2, D2O-
exchangeable), 6.46, 6.52 (2d, 2H, J = 9.7 Hz, 2CH), 6.73 (s, 1H, CH), 7.23-
7.92 (m, 9H, C6H5, C6H4), 10.93 (s, 1H, NH, D2O-exchangeable). MS (m/z, %):
486 (M+˙, 35%), 202 [M+˙-C15H14N3O3 (substituted pyridine fragment), 34%],
130 (indolomethylene fragment, C9H8N, 100%). Anal. Calcd. for C27H26N4O5
(486.53): C, 66.65; H, 5.38; N, 11.51. Found: C, 66.75; H, 5.28; N, 11.31.
Methyl-α-iminocarbonyl(3-amino-5-phenylpyrazolo-4-yl) -3-indolo-
propanoate (15a)
Methyl α-iminocarbonyl(3-amino-1,5-diphenylpyrazolo-4-yl) -3-in-
dolopropanoate (15b)
General Procedure
To a solution of compound 12 (1.86 g, 0.005 mol) in ethanol (30 mL),
containing triethylamine (1 mL, 0.01 mol), either hydrazine hydrate (0.25 g,
0.005 mol) or phenylhydrazine (0.54 g, 0.005 mol) was added. The reaction
mixture, in each case, was heated under reux for 4h then poured over ice/
water mixture and neutralized with hydrochloric acid. The formed solid prod-

J. Chil. Chem. Soc., 54, Nº 2 (2009)
179
uct, in each case, was ltered off, washed with water and crystallized from the
appropriate solvent.
Compound 15a: Yellow crystals, from EtOH, yield 77% (1.55 g), mp 100-
101°C. IR (v/cm-1): 3450-3150 (NH2, 3NH), 3050 (CH-aromatic), 2985, 2865
(CH3, CH2), 1730, 1700 (2C=O), 1660 (C=N), 1630 (C=C). 1H NMR (δ ppm):
3.43 (s, 3H, CH3), 3.56 (m, 2H, CH2), 3.75 (m, 1H, CH), 4.83 (s, 2H, NH2, D2O-
exchangeable), 6.93 (s, 1H, CH), 7.05-7.72 (m, 9 H, C6H5, C6H4), 9.48, 10.91,
10.92 (3s, 3H, 3NH, D2O-exchangeable). MS (m/z, %): 404 (M+˙+1; 70%), 336
(M+˙- C6H5, 50%), 77 (C6H5; 36%). Anal. Calcd. for C22H21N5O3 (403.44): C,
65.49; H, 5.24; N, 17.35. Found: C, 65.32; H, 5.11; N, 17.15.
Compound 15b: White crystals from MeOH, yield 72% (1.72 g), mp
136-137°C. IR (ν/cm-1): 3450-3250 (NH2, 2NH), 3050 (CH-aromatic), 2985,
2685 (CH3, CH2), 1730, 1690 (2C=O), 1660 (C=N), 1630 (C=C). 1H NMR (δ
ppm): 3.43 (s, 3H, CH3), 3.53 (m, 2H, CH2), 3.75 (m, 1H, CH), 4.85 (s, 2H,
NH2, D2O-exchangeable), 6.73 (s, 1H, CH), 6.76-7.80 (m, 14H, 2C6H5, C6H4),
10.37, 10.93, (2s, 2H, 2NH, D2O-exchangeable). Anal. Calcd. for C28H25N5O3
(479.54): C, 70.13; H, 5.25; N, 14.60. Found: C, 69.99; H, 5.11; N, 14.42.
Methyl α-iminocarbonyl(3-amino-5-phenylisooxazolo-4-yl) -3-indolo-
propanoate (16). To a solution of compound 12 (1.86 g, 0.005 mol) in ethanol
(30 mL), containing a catalytic amount of sodium acetate (1.0 g), equivalent
amount of hydroxylamine hydrochloride acid (0.35 g, 0.005 mol) in ethanol
(10 mL) was added with stirring and warming. The solid product formed at
room temperature triturated with ice/water mixture and collected by ltration.
Yellowish crystals, from MeOH, yield 75% (1.51 g), mp 136-137°C. IR (v/
cm-1): 3450-3250 (NH2, 2NH), 3050 (CH-aromatic), 2985, 2865 (CH3, CH2),
1730, 1690 (2C=O), 1660 (C=N), 1630 (C=C). 1H NMR (δ ppm): 3.38 (s, 3H,
CH3), 3.55 (m, 2H, CH2), 3.72 (m, 1H, CH), 4.83 (s, 2H, NH2, D2O-exchange-
able), 6.31 (s, 1H, CH), 7.04-7.71 (m, 9 H, C6H4, C6H5), 10.91, 10.97 (2s, 2H,
2NH, D2O-exchangeable). Anal. Calcd. for C22H20N4O4 (404.43): C, 65.33; H,
4.98; N, 13.85. Found: C, 65.11; H, 4.72; N, 13.79.
α-Imino(acetonitrilocarbamido)-3-indolopropionic acid (17). To a so-
lution of tryptophan 1 (1.02 g, 0.005 mol) in dimethyl formamide (30 mL),
equimolar amount of ethyl cyanoacetate 4b (0.56 g, 0.005 mol) was added.
The reaction mixture was heated under reux for 4h and then was evaporated in
vacuum. The remaining product was triturated with diethyl ether, and the solid
product was collected by ltration. Yellow crystals, from EtOH, yield 79%
(1.07 g), mp 146-147°C. IR (v/cm-1): 3430-3385 (2NH), 3050 (CH-aromatic),
2680 (CH2), 2220 (CN), 1705, 1680 (2C=O), 1620 (C=C). 1H NMR (δ ppm):
3.43 (m, 2H, CH2), 3.49 (s, 2H, CH2CN), 3.75 (m, 1H, CH), 6.95 (s, 1H, CH),
7.01-7.49 (m, 4H, C6H4), 8.75, 8.82 (2s, 2H, 2NH, D2O-exchangeable), 11.15
(s, 1H, OH). Anal. Calcd. for C14H13N3O3 (271.28): C, 61.98; H, 4.83; N, 15.48.
Found: C, 61.77; H, 4.65; N, 15.21.
α-Imino(benzaloacetonitriocarbamido)-3-indolopropionic acid (18).
To a solution of compound 17 (1.35 g, 0.005 mol), in ethanol (30 mL), contain-
ing piperidine (0.85 mL, 0.01 mol), equivalent amount of benzaldehyde (0.53
g, 0.005 mol) was added. The reaction mixture was heated under reux for 3h
then poured over ice/water mixture and neutralized with dilute hydrochloric
acid. The formed solid product ltered off, dried and crystallized from dilute
ethanol. Pale brown crystals, yield 75% (1.21 g), mp 177-178°C. IR (γ/cm-1):
3400-3200 (2NH), 3050 (CH-aromatic), 2865 (CH2), 2200 (CN), 1720, 1690
(2C=O). 1H NMR (δ ppm): 3.53 (m, 2H, CH2), 3.72 (m, 1H, CH), 4.10 (s, 1H,
CH), 6.48 (s, 1H, CH), 7.31-7.72 (m, 9H, C6H4, C6H5), 8.42, 9.11 (2s, 2H, 2NH,
D2O-exchangeable), 11.15 (s, 1H, OH). MS (m/z, %): 359 (M+˙, 35%). Anal.
Calcd. for C21H17N3O3 (359.38): C, 70.18; H, 4.76; N, 11.69. Found: C, 70.31;
H, 4.53; N, 11.45.
α-Imino(phenylhydrazoacetonitrilocarbamido)-3-indolopropionic
acid (19). A solution of compound 17 (1.35 g, 0.005 mol), in ethanol (30 mL),
containing a catalytic amount of sodium acetate (1.0 g) was cooled to 0-5°C
and then gradually with a cold solution of benzenediazonium chloride [pre-
pared by adding sodium nitrite solution (0.7 g, 0.01 mol) to a cold solution of
aniline 0.45 g, 0.005 mol) with continuous stirring]. After addition of diazo-
nium salt was completed, the reaction mixture was stirred at room temperature
for 30 min. The solid product, separated upon dilution with cold water, was
ltered off, washed with water several times, dried and crystallized. Brown
crystals from EtOH, yield 75% (1.40 g), mp 79-80°C. IR (γ/cm-1): 3430-3335
(3NH), 3050 (CH-aromatic), 2865 (CH2), 2200 (CN), 1720, 1690 (2C=O),
1660 (C=N), 1630 (C=C). 1H NMR (δ ppm): 1.27 (s, 1H, CH), 3.28 (m, 2H,
CH2), 3.75 (m, 1H, CH), 5.64 (s, 1H, CH), 7.67-7.74 (m, 9H, C6H4, C6H5), 8.51,
9.32-9.36 (3s, 3H, 3NH, D2O-exchangeable), 11.40 (s, 1H, OH). 13C NMR (δ):
25.0 (CH2), 55.8 (CH), 80.7, 111.6, 113.6, 114.8, 118.6, 120.4, 122.2, 130.4,
133.9 (benzene, pyrrole C), 117.6 (CN), 150.3, 166.4 (2 CO), 177.9 (C=N).
Anal. Calcd. for C20H17N5O3 (375.39): C, 63.99; H, 4.56; N, 18.65. Found: C,
63.78; H, 4.43; N, 18.59.
ACKNOWLEDGEMENT
Mohareb R. M. expressed his deepest thank to the Alexander von Hum-
boldt Foundation for nancing support during his stay in Germany, Stuttgart
University and completing this work.
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